1. Field of the Invention
The present invention relates in general to tools for use in well packer asemblies, and in particular to expendable plugs of the type which are disengaged from a well packer by forces generated through a tubing string.
2. Description of the Prior Art
Typically, plug assemblies for use in subterranean wells are utilized in combination with a packer assembly and are selectively located within a well casing in order to isolate one or more of the production zones of the well. The plug assembly is mounted within a packer assembly at the well head and the entire unit is run down the well casing and secured at a selected location along the casing. When it is desired to release the plug from the packer assembly, a tubing string having a suitable actuator attached to the lower end thereof is run down the well casing to contact the plug. Typically, by applying sufficient downward force to the plug, the plug becomes disengaged from the packer assembly and free falls to the bottom of the well. An example of such an expendable plug is disclosed in U.S. Pat. No. 4,188,999 to A. Amancharia.
While an expendable plug of the type disclosed in the above mentioned patent has proved advantageous in many instances, there are certain instances which may create some problems for the operator. For example, if a measurable amount of sand has accumulated on top of the plug, and the tubing string is lowered to disengage the plug, the tubing string will rest on top of the sand. Although typically a downward force transmitted to the plug through a small amount of sand may be sufficient to release the plug, the operator has no indication at the well head whether the tubing string has actually contacted the plug or whether the tubing string is resting on a substantial depth of sand. Consequently once the plug is released, the operator will have no indication as to the location of the lower end of the tubing string relative to the packer assembly. Since the lower portion of the tubing string is typically provided with external seals to be positioned within the packer assembly after the plug is released, it is difficult for the operator to properly position the external seals within the packer.
One type of prior art expendable plug which is not released upon the initial application of a downward force to the plug is a screw-out plug of the type manufactured by Pengo Industries, Inc. of Forth Worth, Texas. In order to release this type of plug, an actuator attached to the tubing string is lowered down the well casing to engage the plug. After the plug has been contacted, the actuator is rotated to release the plug from the packer. However, the operator is not provided with any initial indication that the actuator has actually located the plug.